Schmidt Jenna M, Royalty Taylor M, Lloyd Karen G, Steen Andrew D
Department of Earth and Planetary Sciences, College of Arts and Sciences, The University of Tennessee, Knoxville, TN, United States.
Department of Microbiology, University of Tennessee - Knoxville, Knoxville, TN, United States.
Front Microbiol. 2021 Sep 17;12:702015. doi: 10.3389/fmicb.2021.702015. eCollection 2021.
Heterotrophic microorganisms in marine sediments produce extracellular enzymes to hydrolyze organic macromolecules, so their products can be transported inside the cell and used for energy and growth. Therefore, extracellular enzymes may mediate the fate of organic carbon in sediments. The Baltic Sea Basin is a primarily depositional environment with high potential for organic matter preservation. The potential activities of multiple organic carbon-degrading enzymes were measured in samples obtained by the International Ocean Discovery Program Expedition 347 from the Little Belt Strait, Denmark, core M0059C. Potential maximum hydrolysis rates (V) were measured at depths down to 77.9mbsf for the following enzymes: alkaline phosphatase, β-d-xylosidase, β-d-cellobiohydrolase, N-acetyl-β-d-glucosaminidase, β-glucosidase, α-glucosidase, leucyl aminopeptidase, arginyl aminopeptidase, prolyl aminopeptidase, gingipain, and clostripain. Extracellular peptidase activities were detectable at depths shallower than 54.95mbsf, and alkaline phosphatase activity was detectable throughout the core, albeit against a relatively high activity in autoclaved sediments. β-glucosidase activities were detected above 30mbsf; however, activities of other glycosyl hydrolases (β-xylosidase, β-cellobiohydrolase, N-acetyl-β-glucosaminidase, and α-glucosidase) were generally indistinguishable from zero at all depths. These extracellular enzymes appear to be extremely stable: Among all enzymes, a median of 51.3% of enzyme activity was retained after autoclaving for an hour. We show that enzyme turnover times scale with the inverse of community metabolic rates, such that enzyme lifetimes in subsurface sediments, in which metabolic rates are very slow, are likely to be extraordinarily long. A back-of-the-envelope calculation suggests enzyme lifetimes are, at minimum, on the order of 230days, and may be substantially longer. These results lend empirical support to the hypothesis that a population of subsurface microbes persist by using extracellular enzymes to slowly metabolize old, highly degraded organic carbon.
海洋沉积物中的异养微生物会产生细胞外酶来水解有机大分子，以便其产物能够被转运到细胞内并用于能量供应和生长。因此，细胞外酶可能会介导沉积物中有机碳的归宿。波罗的海盆地是一个以沉积作用为主的环境，具有很高的有机质保存潜力。在国际大洋发现计划第347航次从丹麦小贝尔特海峡获取的M0059C岩芯样本中，测定了多种有机碳降解酶的潜在活性。对以下几种酶在深度达77.9米海底以下的潜在最大水解速率（V）进行了测定：碱性磷酸酶、β - D - 木糖苷酶、β - D - 纤维二糖水解酶、N - 乙酰 - β - D - 氨基葡萄糖苷酶、β - 葡萄糖苷酶、α - 葡萄糖苷酶、亮氨酰氨肽酶、精氨酰氨肽酶、脯氨酰氨肽酶、牙龈蛋白酶和梭菌蛋白酶。在深度小于54.95米海底时可检测到细胞外肽酶活性，碱性磷酸酶活性在整个岩芯中均可检测到，不过相对于经高压灭菌的沉积物中较高的活性而言较低。在30米海底以上检测到了β - 葡萄糖苷酶活性；然而，其他糖基水解酶（β - 木糖苷酶、β - 纤维二糖水解酶、N - 乙酰 - β - D - 氨基葡萄糖苷酶和α - 葡萄糖苷酶）的活性在所有深度通常都与零无法区分。这些细胞外酶似乎极其稳定：在所有酶中，经过一小时高压灭菌后，酶活性的中位数仍保留51.3%。我们表明，酶周转时间与群落代谢速率的倒数成比例，因此在代谢速率非常缓慢的次表层沉积物中，酶的寿命可能会非常长。一个粗略的计算表明，酶的寿命至少约为230天，而且可能长得多。这些结果为以下假说提供了实证支持：次表层微生物群体通过利用细胞外酶缓慢代谢陈旧、高度降解的有机碳来维持生存。
